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Three types of planar structure microspring electro-thermal actuators with insulating beam constraints
Abstract
A new concept of using an electrically insulating beam as a constraint is
proposed to construct planar spring-like electro-thermal actuators with large
displacements. On the basis of this concept, three types of microspring
actuators with multi-chevron structures and constraint beams are introduced.
The constraint beams in one type (the spring) of these devices are
horizontally positioned to restrict the expansion of the active arms in the
x-direction, and to produce a displacement in the y-direction only. In the
other two types of actuators (the deflector and the contractor), the constraint
beams are positioned parallel to the active arms. When the constraint beams
are on the inner side of the active arms, the actuator produces an outward
deflection in the y-direction. When they are on the outside of the active
arms, the actuator produces an inward contraction. Finite-element analysis
was used to model the performances. The simulation shows that the
displacements of these microspring actuators are all proportional to the
number of the chevron sections in series, thus achieving superior
displacements to alternative actuators. The displacement of a spring actuator
strongly depends on the beam angle, and decreases with increasing the beam
angle, the deflector is insensitive to the beam angle, while the displacement
of a contractor actuator increases with the beam angle.
... A single mechanical binary digit of a MEMS DAC is formed by single Chevron type electro-thermal compliant actuator. The chevron type thermal actuator reported in [6], of length 200µm (L), anchored at an angle of 2.6 0 (ω) is used (Fig 2)for realizing MEMS DAC. The necessary stiffness of the each chevron beam is attained by choosing a suitable width to covert the given binary code. ...
... The working principle of the proposed MEMS based DAC uses the similar principle discussed in [1][2][3][4][5], by using this principle, MEMS based DAC is designed by incorporating chevron type electro-thermal actuators. The deflection of a chevron type thermal actuator depends on the length and the angle of the beams [6], the better deflection is possible when a lesser angle is used. The binary '1' condition ensues when the ETC biased with 5V voltage and it produces the maximum deflection and the binary, '0' ensues when they are not biased. ...
... The inplane deflection of the output beam is the corresponding output of the proposed DAC. Displacement at the output beam of the N-bit MEMSDAC can be estimated from the equation (1) [6]; ...
This paper describes the design and numerical modeling of chevron micro electro thermal compliant (ETC) actuator based Digital to Analogue Converter (DAC). The proposed DAC generate the mechanical displacement at the output from digital electrical input based on the principle of weighted stiffness. The device is made of 4 - horizontal chevron type ETC actuators of different stiffness. The DAC is built using a SOIMUMP’S process steps using MEMS CAD tool COVENTORWARE and its coupled electro-thermo-mechanical analysis is carried out to illustrate the performance. The device operates on 5V which is well suited with conventional CMOS logic and in turn reduces the power consumption of the device.
... A rising temperature will increase the electrical resistance of the device due to the positive temperature coefficient of the resistivity of metals. The average temperature change of the thermal microactuator ΔT ave can be extracted from the change of the resistance by the relation [22] ΔT ...
... The forward displacement is almost proportional to the average temperature. The back bending appears at an average temperature larger than 140 @BULLET C. agreement with theoretical analysis in the literature [12], [22]. For both D1 and D2, the displacement of the tip reached a maximum at a power of 60 mW, specifically at values of ∼16 and 20 μm, respectively; beyond this, the displacement decreased with any further increase in power due to thermal degradation, as discussed later. ...
... The maximum temperature is near the middle of the hot arm. A previous analysis based on the thermal conduction model indicated that the maximum temperature increase of the hot arm ΔT max would be expected to be about 1.5 times the calculated average temperature increase ΔT ave [21], [22]. Assuming an ambient temperature of 20 @BULLET C, the average temperature of 160 @BULLET C shown inFig. ...
In this paper, the thermal degradation of laterally operating thermal actuators made from electroplated nickel has been studied. The actuators investigated delivered a maximum displacement of ca. 20 mum at an average temperature of ~ 450degC , which is much lower than that of typical silicon-based microactuators. However, the magnitude of the displacement strongly depended on the frequency and voltage amplitude of the pulse signal applied. Back bending was observed at maximum temperatures as low as 240degC. Both forward and backward displacements increase as the applied power was increased up to a value of 60 mW; further increases led to reductions in the magnitudes of both displacements. Scanning electron microscopy clearly showed that the nickel beams began to deform and change their shape at this critical power level. Compressive stress is responsible for nickel pileup, while tensile stresses, generated upon removing the current, are responsible for necking at the hottest section of the hot arm of the device. Energy dispersive X-ray diffraction analysis also revealed the severe oxidation of Ni structure induced by Joule heating. The combination of plastic deformation and oxidation was responsible for the observed thermal degradation. Results indicate that nickel thermal microactuators should be operated below 200degC to avoid thermal degradation.
... Microactuators can be designed based on different methods. Electro-thermal, electro-static, pneumatic, piezoelectric and shape memory alloys (SMA) are different actuation mechanisms utilized to achieve this goal [15][16][17][18]. Smart actuators such as piezoelectric and SMA are used more than other types in recent studies because of their functional characteristics, such as ease of activation, high-frequency response, low-cost fabrication, bio-compatibility and high actuation energy density. ...
... In the late 1990s, Kohl et al fabricated a linear microactuator from thin film SMA, then used the same microactuator to manufacture a microgripper [16, 33]. After this, the use of microactuators was considered applicable by researchers in MEMS devices [17, 34]. Given that the stress and strain applied to the SMA microactuators have direct impacts on their performance, they can be appropriately designed and optimized to increase their efficiency. ...
Microactuators are essential elements of MEMS and are widely used in these devices. Microgrippers, micropositioners, microfixtures, micropumps and microvalves are well-known applications of microstructures. In this paper, the design optimization of shape memory alloy microactuators is discussed. Four different configurations of microactuator with variable geometrical parameters, generating different levels of displacement and force, are designed and analysed. In order to determine the optimum values of parameters for each microactuator, statistical design of experiments (DOE) is used. For this purpose, the Souza et al constitutive model (1988 Eur. J. Mech. A 17 789-806) is adapted for use in finite element analysis software. Mechanical properties of the SMA are identified by performing experimental tests on Ti-49.8%Ni. Finally, the specific energy of each microactuator is determined using the calibrated model and regression analysis. Moreover, the characteristic curve of each microactuator is obtained and with this virtual tool one can choose a microactuator with the desired force and displacement. The methodology discussed in this paper can be used as a reference to design appropriate microactuators for different MEMS applications producing various ranges of displacement and force.
... And E F is the electric field. (14) With attention to (14) and (15), function of temperature is: By attention to [16]: Where p r is electrical power; I r is electrical current. Figure 8(e) shows temperature distribution in the gripper. ...
This paper presents a large-stroke, high-precision linear micro motor (LMM); the actuator is authoritative of zero-power latching scheme. Respectively, amount stroke produce by LMM is 2 µm and minimum step size is 100 nm with apply DC voltage of 1.5 volts and 0.4 volts. Large stroke is obtained by repeating the sequence numerous times. LMM composed of four the main part; linear actuator, backers, slider and gripper.
... where, is the coefficient of thermal expansion of silicon, W is the beam width, H is the beam height, and an average temperature rise over the beam can be described [26] as: ...
This paper presents the design, fabrication and characterization of a single-layer out-of-plane electrothermal actuator based on MEMS (Micro-Electro-Mechanical System). The proposed electrothermal actuator is designed to generate motions along the out-of-plane or normal to a wafer by a Joule heating when the current flows through the actuator. This out-of-plane electrothermal actuator is based on a single layer of a SOI (Silicon on Insulator) wafer and two notches near the middle of the actuator beams. Due to these notches, the thermal expansion of the beams in the actuator generates an eccentric loading, which converts into the bending of the beams. This bending of the beam finally generates the out-of-plane motion at the middle of the beam. This behavior is described by the prepared analytic equations and compared by the results from FEM (Finite element Model) analysis. With fabricated samples, a 30 μm displacement is measured along out-of-plane at 5 V driving voltage. The 1st mode of the resonant frequency for the out-of-plane motion is expected to occur at 74.9 kHz from FEA. The proposed actuator is based on the standard SOI-MUMPs (SOI-Multi User Manufacturing Process), so it has good integration capability with other system employing same fabrication techniques. To test its integration capability, a MEMS XYZ stage is fabricated by embedding the proposed out-of-plane electrothermal actuator onto an existing MEMS XY stage. The range of motion of the fabricated XYZ stage is measured about 35 μm x 35 μm x 30 μm along X, Y and Z axes without any changes on its fabrication process.
... In general, a planar-structure electro-thermal actuator may provide an out-of-plane motion [1] or an in-plane motion [2]. The configuration of the structure may be a single bulk material of high thermal expansion coefficient [3] or a thermal bimorph [4]. ...
The present study is aimed to develop an optimization approach which is employed to design an electro-thermal microactuator based on numerical simulation of the device performance. The microactuator basically adopts a bimorph structure which consists of a P-type silicon layer and an aluminum layer. A finite-element multi-physics code (ANSYS 10.0) is used to develop the direct problem solver for predicting the stress/stain, electric, and thermal fields associated with the varying material layers thicknesses during the iterative optimization process. The simplified conjugate-gradient method (SCGM) is used as the optimization method. Regarded as a test case, the modifications of a conventional design, which suffered from high temperature, excessive power consumption, and oxidization of aluminum layer, are attempted. In this study, firstly the direct problem solver is used to predict the performance of various design models so as to select the best one with highest performance. Parametric study of the best design model is then performed, and based on the solutions yielded from the parametric study, the subtle influence of thicknesses of the P-type silicon and the aluminum layers (tS and tAL) on the performance of the microactuator is observed. Finally, the developed optimization approach is applied to predict the optimal combination of the geometrical parameters. The optimal thicknesses of the material layers used in the microactuator are successfully determined, and the optimization process leads to a great improvement in the performance of the microactuator. Results also show that the approach is robust and the obtained optimal combination of the geometrical parameters is independent of the initial guess for the particular case.
... Assuming a rigid-body beam [7] but ignoring the elastic restoring force at the apex where the beam joins the shuttle, one derives ΔL ≈ 2θΔy o for a small tilt angle θ such that sin θ ≈ θ. Combining this with (1), one obtains ...
... This increases the electrical resistance of the device due to the positive temperature coefficient of the metal resistivity. The average temperature of the thermal microactuator, T ave , can be extracted from the change of the resistance by the following equation [18] ...
Metal based thermal microactuators normally have lower operation temperatures than those of Si-based ones; hence they have great potential for applications. However, metal-based thermal actuators easily suffer from degradation such as plastic deformation. In this study, planar thermal actuators were made by a single mask process using electroplated nickel as the active material, and their thermal degradation has been studied. Electrical tests show that the Ni-based thermal actuators deliver a maximum displacement of ~20 m at an average temperature of ~420 °C, much lower than that of Si-based microactuators. However, the displacement strongly depends on the frequency and peak voltage of the pulse applied. Back bending was clearly observed at a maximum temperature as low as 240 °C. Both forward and backward displacements increase with increasing the temperature up to ~450 °C, and then decreases with power. Scanning electron microscopy observation clearly showed that Ni structure deforms and reflows at power above 50mW. The compressive stress is believed to be responsible for Ni piling-up (creep), while the tensile stress upon removing the pulse current is responsible for necking at the hottest section of the device. Energy dispersive X-ray diffraction analysis revealed severe oxidation of the Ni-structure induced by Joule-heating of the current.
... An electro-thermal actuator with planar structure may provide an out-of-plane motion [24] or an in-plane motion [25]. Furthermore, in accordance with the structure of the device, the electro-thermal actuator may be a thermal double-layer microactuator (e.g. the bimetallic structure) or a mechanical thermal expansion microactuator. ...
... Among these available actuation principles, electrothermal actuators are expected to have a very promising future in MEMS applications because they are able to generate rela-tively large displacement and force at a relatively low actuating voltage with a small device area. An electro-thermal actuator with planar structure may provide an out-of-plane motion [1] or an in-plane motion [2]. Furthermore, in accordance with the structure of the device, the electro-thermal actuator may be a thermal double-layer microactuator (e.g. the bimetallic structure) or a mechanical thermal expansion microactuator. ...
The present study is aimed to develop an electro-thermal microactuator. The microactuator adopts a deformable plate with a double-layer structure consisting of a silicon layer and an aluminum layer. As the microactuator is heated by an implanted electric heater, a displacement at the tip of the deformable plate is generated due to the different thermal expansion between these two layers. A serpentine area of N-type silicon is formed by ion implantation in the silicon layer and used as the electric heater. The structure of the microactuator is proposed, modeled, and fabricated in this study. Finite-element analysis is first performed to predict the performance of the microactuator with a multiphysics modeling package (ANSYS 10.0), and then the dimensions of the device are determined. The designed electro-thermal microactuator is fabricated by the semiconductor manufacturing technologies. Experiments on the displacement of the microactuator have been carried out by a microscopic image system to evaluate the performance of the design as well as to demonstrate validity of the modeling.
... , magneto-static [2], electro-static [3] [4] and electro-thermal [5] [6] [7] [8] are popular drive mechanisms implemented in micro-actuators. Piezoelectric material is typically not process-compatible with silicon. ...
Reported presently are two designs to improve the performance of a “chevron” electro-thermal in-plane actuator. One incorporates beams with uniform cross-sections but nonuniform lengths and tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with non-uniform cross-sections to achieve a wider spread of the high temperature “expansion” regions of the beams. With the product of the actuation force and displacement defined as a figure-of-merit, it is verified using finite-element simulation that the incorporation of non-uniform lengths and tilt angles, and non-uniform beam cross-sections leads to respective improvement of 10 and 65% in the figure-of-merit. The effectiveness of these designs was also tested by micro-fabricating actuators occupying fixed device areas.
... While MEMS consist of micrometer-scale components, they have the capability of achieving nanometer displacement resolution and femto- Newton load resolution. In this context, both electrostatic [5] and thermal actuators [6]–[9] were demonstrated as possible actuators. In particular, MEMS actuators have been successfully used in on-chip testing of mechanical properties of MEMS materials [10], [11]. ...
This paper is focused on the dynamic analysis and simulation of a novel microgripper and its components: microcantilever and V-shape thermal actuator. These devices are designed on silicon and implemented on Professional Autodesk Inventor 2014. Simulations were realized using Ansys Workbench Software.
This analysis is common for cantilever, and RF MEM devices, but it is has not been widely realized for other structures, such V-actuator and microgrippers.
The analytical response was acquired with Steady-State Thermal, Static Structural, Modal and Harmonic Response modules.
The dynamic behavior, resonance frequencies of each modal shape and the harmonic behavior with different damping factors of these devices are presented. Parameters as actuation forces, displacements, natural frequencies and specific displacement corresponding to each modal shape in all devices, are also considered in the analysis.
The simulation results show the modal shapes of all analyzed devices, determining their respective modal frequencies and harmonic response. Damping factors of 1% to 10% were employed. The phase angle (± 90º to ±105º) and attenuation levels due to damping were also obtained.
Realizing out-of-plane actuation in micro-electro-mechanical systems (MEMS) is still a challenging task. In this paper, the design, fabrication methods and experimental results for a MEMS-based out-of-plane motion stage are presented based on bulk micromachining technologies. This stage is electrothermally actuated for out-of-plane motion by incorporating beams with step features. The fabricated motion stage has demonstrated displacements of 85 µm with 0.4 µm (mA)−1 rates and generated up to 11.8 mN forces with stiffness of 138.8 N m−1. These properties obtained from the presented stage are comparable to those for in-plane motion stages, therefore making this out-of-plane stage useful when used in combination with in-plane motion stages.
An analytical model that can accurately predict the performance of a polysilicon thermal flexure actuator has been developed. This model is based on an electrothermal analysis of the actuator, incorporating conduction heat transfer. Heat radiation from the hot arm of the actuator to the cold arm is also estimated. Results indicate that heat radiation becomes significant only at high input power, and conduction heat losses to both the substrate and the anchor are mainly responsible for the operating temperature of the actuator under routine operations. Actuator deflection is computed based on elastic analysis of structures. To verify the validity of the model, polysilicon thermal flexure actuators have been fabricated and tested. Experimental results are in good agreement with theoretical predications except at high input power. An actuator with a 240 µm long, 2 µm thick, 3 µm wide hot arm and a 180 µm long, 12 µm wide cold arm deflected up to 12 µm for the actuator tip at an input voltage of 5 V while it could be expected to deflect up to 22 µm when a 210 µm long cold arm is used.
For Part I see L. Que, J.S. Park and Y.B. Gianchandani, ibid.,
vol.10, pp.247-54 (2001). This paper reports on the use of bent-beam
electrothermal actuators for the purpose of generating rotary and
long-throw rectilinear displacements. The rotary displacements are
achieved by orthogonally arranged pairs of cascaded actuators that are
used to rotate a gear. Devices were fabricated using electroplated Ni, p
<sup>++</sup> Si, and polysilicon as structural materials. Displacements
of 20-30 μm with loading forces >150 μN at actuation voltages
<12 V and power dissipation <300 mW could be achieved in the
orthogonally arranged actuator pairs. A design that occupies <1 mm
<sup>2</sup> area is presented. Long-throw rectilinear displacements
were achieved by inchworm mechanisms in which pairs of opposing
actuators grip and shift a central shank that is cantilevered on a
flexible suspension. A passive lock holds the displaced shank between
pushes and when the power is off. This arrangement permits large output
forces to be developed at large displacements, and requires zero standby
power. Several designs were fabricated using electroplated Ni as the
structural material. Forces >200 μN at displacements >100 μm
were measured
This paper describes electrothermal microactuators that generate
rectilinear displacements and forces by leveraging deformations caused
by localized thermal stresses. In one manifestation, an electric current
is passed through a V-shaped beam anchored at both ends, and thermal
expansion caused by joule heating pushes the apex outward. Analytical
and finite element models of device performance are presented along with
measured results of devices fabricated using electroplated Ni and
p<sup>++</sup> Si as structural materials. A maskless process extension
for incorporating thermal and electrical isolation is described. Nickel
devices with 410-μm-long, 6-μm-wide, and 3-μm-thick beams
demonstrate 10 μm static displacements at 79 mW input power; silicon
devices with 800-μm-long, 13.9-μm-wide, and 3.7-μm-thick beams
demonstrate 5 μm displacement at 180 mW input power. Cascaded silicon
devices using three beams of similar dimensions offer comparable
displacement with 50-60% savings in power consumption. The peak output
forces generated are estimated to be in the range from 1 to 10 mN for
the single beam devices and from 0.1 to 1 mN for the cascaded devices.
Measured bandwidths are ≈700 Hz for both. The typical drive voltages
used are ⩽12 V, permitting the use of standard electronic interfaces
that are generally inadequate for electrostatic actuators
A number of in-plane spring-like micro-electro-thermal-actuators with
large displacements were proposed. The devices take the advantage of the
large difference in the thermal expansion coefficients between the
conductive arms and the insulator clamping beams. The constraint beams
in one type (the spring) of these devices are horizontally positioned to
restrict the expansion of the active arms in the x-direction, and to
produce a displacement in the y-direction only. In other two types of
actuators (the deflector and the contractor), the constraint beams are
positioned parallel to the active arms. When the constraint beams are on
the inside of the active arms, the actuator produces an outward
deflection in the y-direction. When they are on the outside of the
active arms, the actuator produces an inward contraction. Analytical
model and finite element analysis were used to simulate the
performances. It showed that at a constant temperature, analytical model
is sufficient to predict the displacement of these devices. The
displacements are all proportional to the temperature and the number of
the chevron sections. A two-mask process is under development to
fabricate these devices, using Si3N4 as the
insulator beams, and electroplated Ni as the conductive beams.
This article investigates rectangular two-beam microelectromechanical thermal actuators and provides a method for their optimization. The thermal actuators investigated consisted of two asymmetric parallel arms,one thin and one wide. Under an electric current load, the thin arm heats and expands more than the wide arm, thereby bending the entire structure. Simplified models of the heat transfer mechanisms are used to determine the temperature profile. From the thermal expressions for expansion of the arms, equations are derived to predict the deflection as well as the buckling loads. Measurements of the actuator deflection as a function of voltage are presented. Design guidelines are introduced for optimization of a thermal actuator.
Surface micromachined polycrystalline silicon thermal micro- actuators
provide large deflections while requiring low drive voltages and
occupying small device areas. The force provided by thermal actuators is
not currently known. Therefore, force testers have been designed and
fabricated. The force testers were used to measure the force of
individual actuators over a range of design parameters including flexure
length, hot arm width, arm separation,and actuator thickness. The force
testers have also been connected to arrays of 2 to 20 actuators coupled
together. Measurements of force tester deflection versus actuator drive
power have been taken. The data shows that individual actuators are
capable of generating greater than 4.8 micronewtons of force with less
than 15 milliwatts of power. The test also show that coupling the
actuators together successfully combines the force of individual
actuators. These measurements allow the creation of a general set of
design rules for efficient thermal actuators.
Thermal actuator-based microtweezers with three different driving configurations have been designed, fabricated and characterized. Finite element analysis has been used to model the device performance. It was found that one configuration of microtweezer, based on two lateral bimorph thermal actuators, has a small displacement (tip opening of the tweezers) and a very limited operating power range. An alternative configuration consisting of two horizontal hot bars with separated beams as the arms can deliver a larger displacement with a much-extended operating power range. This structure can withstand a higher temperature due to the wider beams used, and has flexible arms for increased displacement. Microtweezers driven by a number of chevron structures in parallel have similar maximum displacements but at a cost of higher power consumption. The measured temperature of the devices confirms that the device with the chevron structure can deliver the largest displacement for a given working temperature, while the bimorph thermal actuator design has the highest operating temperature at the same power due to its thin hot arm, and is prone to structural failure.
Force and power characteristics are experimentally measured for three types of toggling microthermal actuators: (i) standard two-arm thermal actuators, (ii) chevron or 'V' type actuators and (iii) chevron actuators with a toggle amplifier. Micro-Newton scale forces and micron scale displacements are experimentally measured using an off-chip probe. For each type of actuator, force versus deflection curves are measured to determine mechanical advantage and maximum ranges. For each type of actuator, work output versus input power curves are measured to determine actuator effectiveness. Different actuator designs are compared in terms of force, displacement, power and effectiveness.
A comprehensive thermal model for an electro-thermal-compliant (ETC) microactuator is presented in this paper. The model accounts for all modes of heat dissipation and the temperature dependence of thermophysical and heat transfer properties. The thermal modelling technique underlying the microactuator model is general and can be used for the virtual testing of any ETC device over a wide range of temperatures (300-1500 K). The influence of physical size and thermal boundary conditions at the anchors, where the device is connected to the substrate, on the behaviour of an ETC microactuator is studied by finite element simulations based on the comprehensive thermal model. Simulations show that the performance ratio of the microactuator increased by two orders of magnitude when the characteristic length of the device was increased by one order of magnitude from 0.22 to 2.2 mm. Restricting heat loss to the substrate via the device anchors increased the actuator stroke by 66% and its energy efficiency by 400%, on average, over the temperature range of 300-1500 K. An important observation made is that the size of the device and thermal boundary conditions at the device anchor primarily control the stroke, operating temperature and performance ratio of the microactuator for a given electrical conductivity.
This paper examines the time and frequency response characteristics of two-arm micromachined thermal actuators. Two types of thermal actuators are considered: hot/cold arm actuators and 'V' or 'chevron' shaped actuators. A heat transfer equation governing the temperature profile along the thermal actuators is derived. Equations for the thermal time constants and the frequency responses are presented. The thermal time constants and frequency responses are measured experimentally and compared to analytical predictions.
At the micro-scale, thermal actuation provides larger forces compared to the widely-used electrostatic actuation. In this paper, we highlight another advantage of thermal actuation, viz. the ease with which it can be utilized to achieve a novel embedded electro-thermal-compliant (ETC) actuation for MEMS. The principle of ETC actuation is based on the selective non-uniform Joule heating and the accompanying constrained thermal expansion. It is shown here that appropriate topology and shape of the structures give rise to many types of actuators and devices. Additionally, selective doping of silicon ETC devices is used to enhance the non-uniform heating and thus the deformation. A number of novel ETC building blocks and devices are described, and their analysis and design issues are discussed. The devices were microfabricated using MCNC’s MUMPs foundry process as well as a bulk-micromachining process called PennSOIL (Penn silicon-on-insulator layer). The designs are validated with the simulations and the experimental observations. The experimental measurements are quantitatively compared with the theoretical predictions for a novel ETC microactuator with selective doping.
Electro-thermal (E-T) actuators have been developed to complement the capabilities of electrostatic actuators. The thermal actuators presented here can be arrayed to generate high forces. Equally significant is that the single actuators and arrays of actuators operate at voltages and currents that are directly compatible with standard microelectronics. This paper demonstrates how combinations of two or more electro-thermal actuators can be applied to a variety of basic building-block micromechanical devices: array of ten lateral actuators; array of ten vertical actuators; vertically actuated two-axis tilting mirror; corner-cube retroreflector actuated by lateral array; grippers over the die edge with flip-over wiring; rotary stepper motor; flip-up optical grating on rotary stepper motor; linear stepper motor; and a linear stepper motor for assembly of hinged structures.
The design, fabrication, and characterization of surface
micromachined piezoelectric accelerometers are presented in this paper.
The thin-film accelerometers employ zinc oxide (ZnO) as the active
piezoelectric material, with different designs using either polysilicon
or ZnO bimorph substrates. Sensitivity analyses are presented for two
specific sensor designs. Guidelines for design optimization are derived
by combining expressions for device sensitivity and resonant frequency.
Two microfabrication techniques based on SiO<sub>2</sub> and Si
sacrificial etching are outlined. Techniques for residual stress
compensation in both fabrication processes are discussed. Accelerometers
based on both processes have been fabricated and characterized. A
sensitivity of 0.95 fC/g and resonant frequency of 3.3 kHz has been
realized for a simple cantilever accelerometer fabricated using the
sacrificial SiO<sub>2</sub> process. Sensors fabricated in the
sacrificial Si process with discrete proof masses have exhibited
sensitivities of 13.3 fC/g and 44.7 fC/g at resonant frequencies of 2.23
kHz and 1.02 kHz, respectively
A new type of MEMS microprobe was designed and fabricated which
can be used for a nest generation wafer probe card. A prototype MEMS
probe card consisting of an array of microprobes individually actuated
by bimorph heating to make contact with the test chip was also
fabricated. This probe card is called the CHIPP (Conformable, HIgh-Pin
count, Programmable) card and can be designed to contact up to 800 I/O
pads along the perimeter of a 1-cm<sup>2</sup> chip with a microprobe
repeat distance of approximately 50 μm. Microprobes for a prototype
CHIPP probe card have been fabricated with a variety of cantilever
structures including Al-SiO<sub>2</sub>, W-SiO<sub>2</sub> and Al-Si
bimorphs, and with the resistive heater placed either inside or on the
surface of the cantilever. Ohmic contacts between tips and bond pads
were tested with contact resistance as low as 250 mΩ. The
deflection efficiency varies from 5.23-9.6 μm/mW for cantilever
lengths from 300-500 μm. The maximum reversible deflection is in the
range of 280 μm. The measured resonant frequency is 8.16 kHz for a
50×500 μm device and 19.4 kHz for a 40×300 μm device.
Heat loss for devices operating in air was found to be substantially
higher than for vacuum operation with a heat loss ratio of about 2/1 for
a heater inside the structure, and 4.25/1 for a structure with the
heater as an outer layer of the cantilever
We examine a new class of sensitive and compact passive strain
sensors that utilize a pair of narrow bent beams with an apex at their
mid-points. The narrow beams amplify and transform deformations caused
by residual stress into opposing displacements of the apices, where
vernier scales are positioned to quantify the deformation. An analytical
method to correlate vernier readings to residual stress is outlined, and
its results are corroborated by finite-element modeling. It is shown
that tensile and compressive residual stress levels below 10 MPa,
corresponding to strains below 6×10<sup>-5</sup> can be measured
in a 1.5-μm-thick layer of polysilicon using a pair of beams that are
2 μm wide, 200 μm long, and bent 0.05 radians (2.86°) to the
long axis of the device. Experimental data is presented from bent-beam
strain sensors that were fabricated from boron-doped single crystal
silicon using the dissolved wafer process and from polycrystalline
silicon using surface micromachining. Measurements from these devices
agree well with those obtained by other methods
In order to extract macroscopic mechanical work out of
microelectromechanical systems, we have proposed the concept of
distributed micromotion systems (DMMS). The key idea of DMMS is to
coordinate simple motions of many microactuators in order to perform a
task. Design, fabrication, and operation of a type of DMMS, called a
ciliary motion system, are presented. A bimorph thermal actuator using
two types of polyimides with different thermal expansion coefficients
and a metallic microheater in between them was fabricated. The
cantilever-shaped actuator curled up from the substrate owing to the
residual stress in polyimides which built up during the cooling process
after they were cured at 350°C. It flattened and moved downward by
flowing current in the heater. The dimensions of the cantilever were 500
μm in length, 100 μm in width, and 6 μm in thickness. The tip
of the cantilever moved 150 μm in the direction vertical to the
substrate and 80 μm in the horizontal direction; these were the
maximum displacements obtained with 33 mW dissipated in the heater. The
cut-off frequency was 10 Hz. On a 1-cm-square substrate, 512 cantilevers
were fabricated to form an array. Two sets of cantilevers were placed
opposing to each other. We operated them in coordination to mimic the
motion and function of cilia and carried a small piece of a silicon
wafer (2.4 mg) at 27-500 μm/s with 4-mW input power to each actuator
Making submicron interelectrode gaps is the key to reducing the
driving voltage of a micro comb-drive electrostatic actuator. Two new
fabrication technologies, oxidation machining and a post-release
positioning method, are proposed to realize submicron gaps. Two types of
actuator (a resonant type and a nonresonant type) with submicron gaps
were successfully fabricated and their operational characteristics were
tested experimentally. The drive voltage was found to be lower than that
of existing actuators. The stability of comb-drive actuators is
discussed
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